The present invention relates to a braking system for a vehicle, and more particularly to a system for automatically supplementing the braking efffort of the service brakes with a drive line brake.
Some vehicles employ a secondary brake in addition to the primary service brakes for positively effecting parking or emergency braking. The secondary or drive line brake on some motor graders, for example, is spring engaged and fluid released and is associated with the vehicles drive line substantially independently of the service brakes. In the event of the loss of absence of sufficient fluid pressure in the vehicle's braking system, the drive line brake is automatically applied. While this is a valuable feature, the capacity of the drive line brake in not utilized during normal actuation of the four fluid engaged and spring released service brakes which are individually located in each of the tandem wheels of the motor grader. This means that the number of service brakes, or the total capacity of the service brakes must be sufficient to provide full braking of the vehicle under normal driving conditions which results in additional expense and a waste of labor and materials.
In view of the above, it would be advantageous to provide a control system that will release fluid pressure to the drive line brake and increase fluid pressure to the service brakes under preselected conditions of operation for effectively utilizing the additional available capacity of the drive line brake during normal service braking.